UV-Cured Methyl Methacrylate Electrolyte Prepared by Ultrasonic Spray Deposition

In this study, gel polymer electrolytes (GPE) containing lithium salts were fabricated using an ultrasonic spray deposition (USD) technique. Methyl methacrylate (MMA) was dissolved in propylene carbonate (PC) as the polymer precursor, with IRGACURE-184 employed as the photoinitiator and phenothiazine as the stabilizer. Lithium perchlorate (LiClO₄) and lithium chloride (LiCl) were introduced as lithium-ion sources, separately. The precursor solutions were stirred at 60 °C for 12 h prior to film deposition to ensure homogeneity. The structural and electrochemical properties of the resulting electrolyte films were systematically characterized using UV-Vis-NIR spectroscopy, electrochemical impedance spectroscopy (EIS), optical microscopy, and scanning electron microscopy (SEM). The effects of processing parameters, including lithium salt type, lithium salt concentration, spray flow rate, and number of spray coats, on the optical transmittance and ionic conductivity were investigated. The results demonstrate that ultrasonic spray deposition enables the fabrication of uniform electrolyte films with high material utilization and scalability, making it suitable for low-dose thin-film deposition. The maximum optical transmittance values of the electrolyte films reached 60% for LiClO₄ and 65% for LiCl, respectively. In terms of electrochemical performance, the ionic conductivity of LiClO₄-based electrolyte films reached 1.075 × 10^-7 S cm^-1, which is significantly higher than that of LiCl-based films (6.151 × 10^-7 S cm^-1). Furthermore, mechanical characterization revealed that both LiClO₄ and LiCl electrolyte films exhibited hardness values exceeding 1.6 GPa and elastic moduli greater than 2.8 GPa, indicating good mechanical stability. These results suggest that the developed gel polymer electrolyte films prepared by ultrasonic spray coating exhibit promising properties for applications in electrochemical and electrochromic devices.